The present invention relates in general to Transient Voltage Suppression (TVS) devices and, more particularly, to low voltage TVS devices.
Virtually all electronic devices are susceptible to transient perturbations such as electrostatic discharge or electromagnetically coupled interference. The perturbations most often occur at the Input/Output (I/O) interfaces to the electronic devices. Typical examples of I/O interfaces susceptible to the transient perturbations, or signals, are power supply input terminals and data bus terminals to name only a few.
Zener or avalanche diodes, to be referred to as TVS junction diodes, have typically been used to protect the electronic devices from damage caused by the transient voltage signals. TVS junction diodes placed into electronic devices for transient suppression are reverse biased under normal, non-transient conditions. During transient conditions, however, the reverse bias voltage exceeds the reverse breakdown voltage and the TVS junction diode clamps the transient voltage to be equal to the reverse breakdown voltage of the diode, thereby preventing the transient voltage from exceeding the maximum voltage that can be sustained by the electronic device.
Prior art TVS junction diodes perform well for high voltage ( greater than 5 volt) applications, but pose specific detrimental characteristics in low voltage ( less than 5 volt) applications. The detrimental characteristics of low voltage TVS junction diodes include high leakage current and high capacitance. Battery operated electronic devices using TVS junction diodes for transient voltage protection are particularly vulnerable to leakage current caused by the TVS junction diode, since the battery provides limited current capability. TVS junction diodes operating in the low ( less than 5 V) voltage range typically demonstrate leakage current in the milliamp (mA) range.
Electronic devices today are designed to operate at battery supplied potentials below 5 volts, such as 3 volts and 1.8 volts or even lower. The current requirements of the battery operated circuits are being driven lower as well. TVS junction diode protection devices are no longer acceptable in the lower voltage ranges due to the excessive leakage current properties below 5 volts. Prior art TVS devices, such as a punch-through, 3-layer devices, while achieving low voltage protection at low leakage current, exhibit several undesirable characteristics, such as negative resistance, or snapback, and lack of punch-through voltage control. Consequently, the punch-through voltage obtained from device to device is randomly distributed.
Hence, there is a need for a TVS device capable of operation in the sub-5 volt range, with no snapback, acceptable leakage current and low capacitance, having tight control over the clamping voltage.